An acrylic rubber composition, which is excellent in heat resistance and oil resistance, has been widely used as a hose part or a sealing article in an engine room of an automobile. However, along with exhaust emission controls, a trend toward higher output power of engines, etc. in recent years, conditions under which a hose part or a sealing component is used become severer, and one having a higher heat resistance has been desired.
Such a hose component and a sealing component are further required to have physical properties such as normal state physical properties and compression set. Further, in recent years, in order to improve the productivity, reduction of scorching has been desired for the purpose of improving the vulcanization rate and the productivity.
As an acrylic rubber composition satisfying such requirements, one containing a carboxy group as a crosslinkable site has been known (e.g. Patent Document 1).
In vulcanization of an acrylic rubber composition containing a carboxy group as a crosslinkable site, diamine vulcanization is generally considered to be preferred in view of required physical properties of a vulcanized product. Particularly, it has been known that as a vulcanization accelerator, 2,3,4,6,7,8,9,10-octahydropyrimido(1,2-a)azepine or its salt is effective (e.g. Patent Document 2).
Such a vulcanization accelerator is to improve various physical properties of an acrylic rubber composition, however, its improving effects are still insufficient. Particularly, 2,3,4,6,7,8,9,10-octahydropyrimido(1,2-a)azepine is a strongly basic liquid compound and is difficult to handle, and is problematic in workability such that kneading by an open roll mill is hardly carried out. Further, 2,3,4,6,7,8,9,10-octahydropyrimido(1,2-a)azepine salts are usually liquids, but are deliquescent even if they are solids, and accordingly they are problematic in workability in the same manner as the above compound. Further, the balance of normal state physical properties, compression set, heat resistance, etc. of an acrylic rubber composition to be obtainable is still insufficient.
Patent Document 1: JP-A-11-100478
Patent Document 2: JP-A-11-080488